1. Field of the Invention
The present invention relates to an electronic appliance and more particularly relates to a display device or a sensor to be driven while addressing a portion of an electronic appliance.
2. Description of the Related Art
Various types of flat-panel displays have recently been developed as display devices for use in consumer electronic appliances including audiovisual systems such as TVs, office automation equipment, and mobile electronic units like cell phones. Among other things, liquid crystal displays (LCDs), which use a liquid crystal material as its display medium, have been remarkably popularized these days because LCDs are lightweight and thickness-reduced display devices with low power dissipation. As a result, the best LCD can now be picked from multiple types according to its intended application.
Examples of those different types include transmission-type LCDs, reflection-type LCDs, and projection-type LCDs. Specifically, a transmission-type LCD includes a backlight behind its LCD panel and allows the viewer to sense the light that has been emitted from the backlight and then transmitted through the LCD panel. A reflection-type LCD includes a reflector on the back surface or inside of its LCD panel and allows the viewer to sense the light that has come externally and has been reflected from the LCD panel. A projection-type LCD (i.e., a liquid crystal projector) projects an image from its LCD panel onto a screen by using a projection lamp and allows the viewer to sense the projected image on the screen.
Flat-panel displays include not only those LCDs but also several other types of electronic display devices that conduct a display operation according to mutually different principles. Examples of those display devices include EL display devices (self-emitting display devices) that use an EL emission layer, toner display devices and electrophoretic display devices aiming at so-called “electronic paper displays”, and twisted ball display devices. The toner display devices, electrophoretic display devices and twisted ball display devices are reflective display devices that utilize reflection of externally incoming light.
Although their display principles (or methods) are different, each of these display devices normally conducts a display operation by an active-matrix addressing technique when their required display capacity (i.e., the number of pixels) is relatively large. In active-matrix addressing, an active-matrix substrate (or addressing substrate), on which each pixel is provided with a switching element (or active component), is used to select a specific location to be addressed. A display device that uses such an addressing substrate (or active-matrix substrate) is described in detail in “Liquid Crystal Display Technologies for Active-Matrix LCDs”, edited by Shoichi Matsumoto, Sangyo Tosho Kabushiki Kaisha (publisher of books on industrial technologies), Nov. 8, 1996.
FIG. 8 schematically illustrates the cross-sectional structure of a typical known liquid crystal display device 400. Only the LCD panel portion of the device 400 is shown in FIG. 8 and the illustration of the backlight, polarizers, peripheral drivers, power supply and other members thereof is omitted for the sake of simplicity.
As shown in FIG. 8, the liquid crystal display device 400 includes a pair of substrates 62 and 71 and a liquid crystal layer 63, which is sandwiched between the substrates 62 and 71. The substrates 62 and 71 are typically glass substrates. The liquid crystal layer 63 is formed by sealing the gap between the substrates 62 and 71 with a seal member 69. On the surface of the substrate 71, gate lines 74, source lines 75, switching elements (typically TFTs) 76 and pixel electrodes 73 are provided so as to face the liquid crystal layer 63. Each of the pixel electrodes 73 is connected to associated one of the source lines 75 by way of associated one of the switching elements 76. On the surface of the other substrate 62, a counter electrode 64 is provided so as to face the liquid crystal layer 63. If necessary, alignment films and/or a color filter layer may be provided for these substrates 62 and 71.
This liquid crystal display device 400 may be driven in the following manner. Specifically, a number of switching elements 76 on the same row are selectively turned ON responsive to a gate signal that has been supplied through one of the gate lines 74. Then, a predetermined display signal (or gray-scale signal) is supplied through one of the source lines 75 to the pixel electrode 73 that is connected to one of the ON-state switching elements 76. That is to say, multiple pixels, which are arranged in matrix (or in columns and rows) for the respective pixel electrodes 73, are addressed one gate line 74 after another by a line sequential technique. A common voltage is applied to the counter electrode 64. A voltage corresponding to a potential difference between the addressed (or selected) one of the pixel electrodes 73 and the counter electrode 64 is applied to a portion of the liquid crystal layer 63 corresponding to the pixel selected. Liquid crystal molecules in the liquid crystal layer 63 exhibit optically anisotropic properties, i.e., change their orientation directions with the voltage applied thereto. By utilizing this phenomenon, the incoming light is modulated by the liquid crystal molecules while being transmitted through the liquid crystal layer 63. In this manner, the liquid crystal display device 400 conducts a display operation.
There are other types of active-matrix-addressed liquid crystal display devices. For example, a so-called “counter source” type liquid crystal display device is also known in the art. In the “counter source” type liquid crystal display device, a common voltage is applied to the pixel electrodes and a display signal is supplied to multiple counter electrodes, which are provided as a parallel striped arrangement of source lines.
The active-matrix-addressed liquid crystal display device can certainly display an image of quality but is still relatively expensive.
This is partly because a huge number of switching elements should be provided for the addressing substrate. Also, in the conventional structure shown in FIG. 8, the addressing substrate may cause a failure even after the addressing substrate is complete. For example, defects may be produced in the process step of bonding the two substrates 62 and 71 together or in the process step of injecting a liquid crystal material into the gap. In such an undesirable situation, the production yield of liquid crystal display devices decreases while the manufacturing cost thereof increases.
Furthermore, it is an increasingly pressing worldwide demand to contribute to the protection of global environments by utilizing or recycling the materials and components as efficiently as possible. In the conventional liquid crystal display device 400 shown in FIG. 8, however, the substrates 62 and 71 are strongly adhered together with the seal member 69. Accordingly, it is difficult to separate and recycle only the addressing substrates 71, for example.
The active-matrix-addressed liquid crystal display device has these problems but organic EL display devices and other types of display devices also have similar problems. Likewise, these problems are also shared by other sensors and input devices that use an addressing substrate, not just the display devices. That is to say, these are problems to be commonly encountered in any of various types of electronic appliances that are designed to drive an array of elements by using an addressing substrate. As used herein, the “array of elements” normally refers to an array of display area units (or pixels) but may also mean an array of capacitance sensors. Also, although the conventional liquid crystal display device 400 is addressed by a line sequential technique, a point sequential technique may also be used as an alternative addressing technique. Furthermore, the addressing technique is not necessarily an electrical one but may also be an optical one.